A driving motor with a stator winding that can be switched over from a single-phase or multi-phase network to a dc network, in whose stator field a squirrel-cage rotor and, together with it, a magnetic rotor mounted on the motor shaft are arranged, is described in French Preliminary Published Patent Application No. 23,86,184. The number of poles and the pole pitch of the magnetic rotor, designed with diametral magnetization direction, correspond to the stator winding poles that can be excited with direct current. The poles of the magnetic rotor are oriented toward the opposite poles of the stator winding when direct current flows through these poles.
The stator winding of the driving motor can be switched over from single-phase or multi-phase network to a direct-current network for different modes of operation, but the manner in which this is done is not specified.
Even though designing the driving motor with a magnetic rotor in which the number of poles and the pole pitch correspond to the stator winding makes it possible, for example, for a stator winding with three phase windings, which is common in asynchronous motors, to decelerate the magnetic rotor in dc operation and to hold it by the stator poles, in whose action zone the rotor poles come to a stop, it is impossible to stop the auxiliary rotor in a predetermined position with the means known from this preliminary published patent application in the case of such a stator winding.
A driving motor, whose stator has a winding consisting of two or more phase windings, is known from West German Offenlegungsschrift No. DE-OS 32,29,351. A plurality of rotors are fastened on the motor shaft one behind the other in the axial direction in the stator field, and at least one of these [rotors] is designed as a squirrel-cage rotor and at least one is designed as a synchronous rotor excited by permanent magnets. In the synchronous rotor, a soft iron yoke, which carries two half-ring-shaped permanent magnets, is arranged on a hub made of nonmagnetizable material.
Even though a similar design of the stator as well as the different rotors are described in this Offenlegungsschrift, the manner in which the stator winding is operated to drive the rotor is not mentioned at all.
West German Offenleguingsschrift No. DE-OS 19,47,721 describes a three-phase squirrel-cage motor, on whose shaft an armature disk rotor is arranged nonrotatably. The rotor is supplied with direct current via carbon brushes and is subject to an axially directed magnetic field of a second stator. Positioning is performed by the armature disk rotor when the speed of the motor shaft drops below an adjustable speed limit during deceleration.
It is disadvantageous in such drive motors that different stators are needed for the different modes, such as continuous operation or positioning operation, which makes the drive motor more complicated and expensive. The additional stator also increases the weight.
The construction and the mode of operation of a self-commutated converter is described in the book Elektrotechnik fur Maschinenbauer by H. Linse (Teubner-Verlag, Stuttgart, 6th revised edition, pp. 303 and 304). One of these self-commutated converters is represented according to FIG. 303.1 of this publication as the control unit of an asynchronous three-phase squirrel-cage motor. A dc intermediate circuit is supplied with constant voltage via a rectifier that is connected to a three-phase power net. A three-phase pulse invertor is connected to this intermediate circuit.
The required alternating current of any desired frequency can be produced by the pulse invertor, according to the subharmonic method for example. The direct voltage received is sent to the stator winding in the form of square pulses of different polarizations and different pulse times, so that a sinusoidal oscillation of the desired frequency and amplitude is obtained as a subharmonic.
Using such a converter, it is possible to vary the speed of a three-phase squirrel-cage motor within a relatively broad range.
A stepper motor whose stator has poles arranged at equal angular offsets, each of which is wound with a coil, is described in West German Preliminary Published Patent Application No. DE-OS 25,42,395. The coils are connected so that two adjacent coils always act on a rotor whose magnetic axis is defined by a permanent magnet or a rotor body of variable magnetic resistance. As a result, the rotor is positioned in a resting position that is predetermined by the resultant effect of the two coil fields. If further coils are energized one after another in the predetermined nominal direction of rotation of the rotor, the rotor is always turned further through an angle predetermined by the distance between the coils.
Even though such stepper motors are excellent for positioning, acceleration and deceleration processes between two resting positions these stopper motors have a disadvantageous effect for continuous operation. In addition, stepper motors are relatively sophisticated and expensive because of their complicated design and are uneconomical beyond a certain power limit.